The purpose of the stands of a surgical microscope is on the one hand to hold the microscopes securely, and on the other hand to ensure counterbalanced positioning of the surgical microscope. This counterbalancing is usually achieved by way of displaceable counterweights so that, despite changeable loads, the microscope is easily positionable in three dimensions.
DE 43 20 443 A1 discloses a stand for a surgical microscope that uses displaceable weights for weight compensation. Also presented in this document is a motorized X-Y positioning unit that is arranged on the stand and carries the surgical microscope. The motorized X-Y positioning unit comprises two carriages that are embodied movably via a DC motor and a linkage. This X-Y positioning unit is evidently used in this document to carry out an automatic fine balancing of the surgical microscope.
An X-Y positioning unit of this kind can also be used in a counterbalanced microscope or stand to move the surgical microscope over the surgical site in the X and Y directions so as thereby to establish a different image area during the operation.
The existing solution provides, for such displacement by an X-Y positioning unit, DC motors having an encoder and linkage. These solutions have proven to function well, but because of the many components are very complex and of correspondingly large dimensions. The linkages furthermore cause noise, which has been reduced by way of so-called solid-borne sound dampers. An apparatus for securing a solid-borne sound-transferring component is depicted and described in DE 10 2005 014 376 (not previously published).
Previous attempts to replace the DC motors having a separate linkage and encoder with stepper motors of simple construction having an integrated spindle or drive shaft failed because the individual steps of the motors resulted in a jerky motion in the image. Jerky motions in the image are, however, unacceptable to a surgeon. The jerky motion furthermore causes an oscillation of the moving mass and consequently an excitation of the system, in particular of the microscope. The microscope, weighing approximately 15 kg, begins to oscillate slowly, and the result is an unstable image for the surgeon. The microscope continues to oscillate even after the stepper motor is shut off. This has proven to be unusable in practice.